The term "tape roll" is used in the present invention to indicate a flexible, narrow, long band-like member, such as a magnetic tape, e.g., a video tape or an audio tape, or a movie film, e.g., Single 8, Super 8, etc. which is wound in the form of a roll.
Tape rolls are usually placed in a case referred to as a cassette or magazine (cartridge), and are wound and re-wound in the case. Between the tape roll and an inner surface of the case, therefore, friction may be produced, preventing the tape from running smoothly. Thus, a material having a low frictional resistance, generally called a friction sheet, is fixed or rotatably provided on the inner surface of the case which is subject to sliding contact with the tape roll.
It is therefore required for such friction sheets to have a low coefficient of friction, good abrasion resistance, and dimensional stability, and, sometimes, antistatic properties.
Friction sheets which have heretofore been known include a fluorine resin sheet, a silicone-processed or wax-processed paper, a sheet prepared by incorporating a fluorine compound into the surface of a thermoplastic resin film, as described in Japanese Patent Application (OPI) No. 145482/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and a sheet coated with at least one of a low molecular weight polyethylene or an alkyl sulfate sodium salt as described in Japanese Utility Model Publication No. 2858/68.
These conventional friction sheets, however, are not always satisfactory in abrasion resistance and surface stability. In particular, friction sheets containing fluorine have the disadvantages that the moldability is poor, and production costs are high because of expense of fluorine.
Furthermore, friction sheets which have been known in recent years include a sheet consisting of a single layer comprising a uniaxially or biaxially oriented high density polyethylene film as described in German Patent Application No. 3111330 (which refers to U.S. patent application Ser. No. 247,030, filed Mar. 24, 1981). Such friction sheets have been expected to be additionally improved in coefficient of friction and abrasion resistance properties, and more economical.